The present invention relates generally to disc brake rotors as used in a vehicle braking system. More particularly, the invention relates to a vehicle brake rotor that incorporates a plurality of vanes designed to reduce noise generated in the brake system.
Noise generated during a brake application has been increasing as the size of vehicles has been decreasing. Attempts have been made to reduce the noise generated using various systems and methods. One such technique involves the use of sound adsorption coatings on the pad assembly. While such coatings have some effectiveness, the addition of the coating adds cost to the manufacture and at times, undesirable noise occurs when the thickness of the coating has not been uniform.
Another technique involves a disc brake pad assembly having clench tabs extending through rubber-like grommets in openings in a caliper housing leg so that the grommets are retained in the openings and the brake pad assembly is retained on the housing leg. The grommets provide a noise damping action during braking to reduce noise.
Individual noise problems have been reduced through the modification of the ingredients in the composition of materials that make up a brake pad. In many of these cases, while noise may have been abated somewhat, the braking effectiveness of the system has been changed by the modification of the brake pad material. Still another technique of reducing brake noise involves affixing a ring damper about a periphery of a brake rotor in a disc brake system. The ring damper is held in place by a groove formed in the periphery of the disc and is pre-loaded against the rotor both radially and transversely.
The above techniques involve the reduction of noise by absorbing or masking the noise after it has been created or by adding costly complexity to the braking system. It would be advantageous to design the system to reduce the potential for the creation of noise. It has been suggested that much of brake squeal or noise is influenced by the excitation of the natural frequencies of a rotor caused by the rubbing of friction pads on a rotor surface. There is evidence that a disc brake rotor may have a dozen or more naturally occurring frequencies. While most of these are in the axial direction, others are in the torsional direction. In simulated braking applications only certain of these natural frequencies create brake noise or squeal. Every natural frequency of a vibrating system has associated with it a mode shape that describes the pattern of deformation associated with that natural frequency. In a continuous structure, the mode shape is generally accepted or described by defining the pattern of nodes (loci of points of zero deformation) on the surface of the structure. Experiments have shown that the mode shape of an annular circular plate, a shape like that of a brake rotor, consists of nodal circles and diameters. Thus, a beneficial effect on brake noise should be attainable if the nodal diameter modes of an installed disc rotor are maintained at a maximum separation, thereby reducing or eliminating coupling of the nodal diameter modes in the audible frequency range.
A typical structure of a brake rotor includes a central disc portion that is adapted to be mounted to an axle of a vehicle as in known in the art, by fasteners. An extending portion typically connects one of a pair of rotor friction plates or cheeks to the central disc portion. A plurality of vanes extend from an inner surface of the first plate to connect a second plate thereto. The vanes are typically arranged in a radial fashion about the rotor. The vanes hold the first and second plates in a parallel, side-by-side relationship. Typically, vanes have an overall regular elongate, rod, coffin or rectangular shape with a generally constant width and cross-sectional area. In other words, many current vanes start out a rectangular cross-section at one end and remain rectangular throughout the longitudinal distance of the vane at an opposite end. Similarly, a prior-art plate typically has a thickness or cross-section remaining substantially constant along the radial direction.
One aspect of the present invention provides a disc brake including a pair of friction plates arranged coaxially in a parallel, spaced-apart relationship and a plurality of vanes extending between the pair of friction plates, each of said vanes having a proximal end, a distal end and a mid-portion extending between the proximal end and the distal end, at least one of the distal end and the proximal end of at least half the vanes having a first cross-sectional area, the mid-portion having a second cross-sectional area, the first cross-sectional area being substantially greater than the second cross-sectional area.
In other aspects of the invention the cross-sectional area of the distal end of at least half the vanes can be substantially greater than the cross-sectional area of the mid-portion. The cross-sectional area of the distal end of at least half the vanes can be about 50 percent greater than the cross-sectional area of the mid-portion. The cross-sectional area of the distal end of all of the vanes can be substantially greater than the cross-sectional area of the mid-portion. The cross-sectional area of the distal end of all of the vanes is substantially greater than the cross-sectional area of the mid-portion.
Another aspect of the present invention provides a rotor for a disc brake having a plurality of first vanes alternated with a plurality of second vanes, the first and second vanes both having distal and proximal ends, the distal and proximal ends connected by an extending mid-portion. A cross-sectional area of the mid-portion of the first vanes can be substantially greater than a cross-sectional area of the proximal end. A cross-sectional area of the distal end of the first vanes can be substantially greater than the cross-sectional area of the mid-portion. A cross-sectional area of the mid-portion of the second vanes can be substantially less than a cross-sectional area of both the distal and proximal ends.
Another aspect of the present invention provides a rotor for a disc brake including a mid-portion having a substantially constant longitudinal cross-sectional area. The mid-portion of the vanes can have a narrow portion adjacent the proximal end of the vanes having a cross-sectional area less than that of a portion extending outwardly from the narrow portion of the mid-portion of the vanes.
Another aspect of the present invention provides a rotor for a disc brake including a pair of friction plates arranged coaxially in a parallel, spaced-apart relationship and a plurality of vanes extending between the pair of friction plates, each of the vanes having a proximal end, a distal end and a mid-portion extending between the proximal end and the distal end, at least half of the vanes including a T-shaped portion adjacent the distal end of the vanes.
Other aspects of the present invention provide a rotor wherein all of the vanes include a T-shaped portion adjacent the distal end of the vanes. Half of the vanes of the rotor including a T-shaped portion can include an additional inverse T-shaped portion adjacent the proximal end of the vanes. The T-shaped portion can be at least 50% wider than a width of the mid-portion. Each vane can include an angled portion located between the T-shaped portion and the mid-portion. In an alternate aspect of the present invention all of the vanes can include a T-shaped portion adjacent each respective distal end.
Another aspect of the present invention provides a rotor wherein each of the pair of friction plates includes a chamfer on an inner surface of each friction plate, the chamfer being located adjacent the periphery of the rotor, the vanes being thicker at the chamfer to extend between the pair of plates.
Another aspect of the present invention provides a rotor for a disc brake including a pair of friction plates arranged coaxially in a parallel, spaced-apart relationship and a plurality of vanes extending between the pair of friction plates, each of said vanes having a proximal end, a distal end and a mid-portion extending between the proximal end and the distal end, at least half of the vanes including an hourglass shaped portion.
Other aspects of the invention provide a rotor where the hourglass shaped portion extends along an entire length of the vanes. The hourglass shaped portion can extend from the mid-portion to the distal end of the vanes. Half of the vanes can include an hourglass shaped portion extending along an entire length of the vanes and the other half of the vanes include an hourglass shaped portion extending from a mid-portion to a distal end of the vanes. A width of the vanes can taper from a distal end along a mid-portion of the vanes at a location adjacent the friction plates. A central portion of the vanes located halfway between the friction plates can have a constant width from the distal end along the mid-portion of the vanes. Each of the vanes can include an increased draft portion having a first thickness located adjacent the distal end of each vane and a second thickness at a mid-portion of each vane, the first thickness being greater than a second thickness.
An aspect of the present invention includes a method of reducing noise in a disc brake rotor including stiffening a radially outer portion of the brake rotor with an outer portion of a plurality of vanes and reducing coupling of nodal diameter modes in an audible frequency range. The outer portion of the plurality of vanes can include a T-shaped portion.
Another aspect of the invention includes a rotor for a disc brake including means for stiffening a radially outer portion of the brake rotor with an outer portion of a plurality of vanes and means for reducing coupling of nodal diameter modes in an audible frequency range. The outer portion of the brake rotor can include a T-shaped portion.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.